Weird lines across model when rendered in low resolution
I suspect the image textures are scaled down. The light marks are the "background" color of the image texture you are using. They appear precisely where your seams are.

I'm sure there is some setting that does this and it may not be a default setting.

You could work around this by dragging in the seams in your image texture more towards the center or maybe find an option, so the image texture won't be scaled down. Alternatively you could render at a higher resolution and later manually scale it down.